Hybrid automatic repeat request (harq) in listen before talk systems

ABSTRACT

Systems and methods presented herein provide for increasing a contention window of a UE employing a LTE communications operating in a radio frequency (RF) band comprising a conflicting wireless technology. In one embodiment, an eNodeB receives a transport block of data from a user equipment (UE). The transport block includes a cyclic redundancy check (CRC). The eNodeB then determines a checksum of the transport block based on the CRC, fails the checksum, and transmits a non-acknowledgement (NACK) of the transport block to the UE based on the failed checksum. The UE, in response to the NACK, increases a contention window and re-transmits the transport block to the eNodeB.

CROSS REFERENCE TO RELATED APPLICATIONS

This patent application is a continuation of U.S. patent applicationSer. No. 15/569,153, filed Oct. 25, 2017, which application is anational stage application of PCT Application No. PCT/US16/32569, filedMay 14, 2016, which application claims priority to, and thus the benefitof an earlier filing date from, U.S. Provisional Patent Application No.62/161,443, filed May 14, 2015, the entire contents of which are herebyincorporated by reference.

BACKGROUND

Cellular telephony continues to evolve at a rapid pace. Cellulartelephone networks currently exist in a variety of forms and operateusing a variety of modulations, signaling techniques, and protocols,such as those found in 3G and LTE networks (3rd Generation of mobiletelecommunications technology and Long Term Evolution, respectively). Asconsumers require more capacity, the networks evolve. For example, somecarriers, or Mobile Network Operators (MNOs), employ a combination of 3Gand the faster LTE because MNOs needed faster networks to satiate theincreased demand for data and voice.

Moreover, efforts exist to implement these technologies in radiofrequency (RF) bands that comprise conflicting communications. Forexample, there has been accelerated development of LTE in unlicensedbands (a.k.a. LTE-U and Licensed-Assisted-Access, or “LAA-LTE”) whereWiFi has traditionally been implemented. Unlike LTE, however, WiFiemploys a method of Listen Before Talk (LBT) to ensure that WiFi systemsdo not interfere with one another. With LBT in WiFi, a WiFi nodedetermines that a transmission is successful if it receives anacknowledgement (ACK) shortly after the transmission. The lack of an ACKmeans that a collision has occurred and the WiFi node doubles itscontention window and re-contends for the channel. However, becauseHybrid Automatic Repeat Request (HARQ) ACKs and non-acknowledgements(NACKs) are sent in 3 subframes (i.e., 3 ms after the transmission ofdata), LTE systems have difficulty changing a contention window size.

SUMMARY

Systems and methods presented herein provide for increasing a contentionwindow of a UE employing LTE communications operating in an RF bandcomprising a conflicting wireless technology. In one embodiment, aneNodeB receives a transport block of data from a user equipment (UE).The transport block includes a cyclic redundancy check (CRC). The eNodeBthen determines a checksum of the transport block based on the CRC,fails the checksum, and transmits a non-acknowledgement (NACK) of thetransport block to the UE based on the failed checksum. The UE, inresponse to the NACK, increases a contention window and re-transmits thetransport block to the eNodeB.

The various embodiments disclosed herein may be implemented in a varietyof ways as a matter of design choice. For example, some embodimentsherein are implemented in hardware whereas other embodiments may includeprocesses that are operable to implement and/or operate the hardware.Other exemplary embodiments, including software and firmware, aredescribed below.

BRIEF DESCRIPTION OF THE FIGURES

Some embodiments of the present invention are now described, by way ofexample only, and with reference to the accompanying drawings. The samereference number represents the same element or the same type of elementon all drawings.

FIG. 1 is a block diagram of an exemplary wireless telecommunicationssystem operating in an RF band with a conflicting wireless system.

FIG. 2 is a flowchart illustrating an exemplary process operable with aneNodeB in the wireless telecommunications system.

FIG. 3 is a flowchart illustrating an exemplary process operable with aUE in the wireless telecommunications system.

FIGS. 4-6 are exemplary messaging diagrams between a UE and an eNodeB inthe wireless telecommunications system.

FIG. 7 is a flowchart illustrating another exemplary process operablewith an eNodeB in the wireless telecommunications system.

FIG. 8 is a flowchart illustrating another exemplary process operablewith a UE in the wireless telecommunications system.

FIG. 9 is a block diagram of an exemplary computing system in which acomputer readable medium provides instructions for performing methodsherein.

DETAILED DESCRIPTION OF THE FIGURES

The figures and the following description illustrate specific exemplaryembodiments of the invention. It will thus be appreciated that thoseskilled in the art will be able to devise various arrangements that,although not explicitly described or shown herein, embody the principlesof the invention and are included within the scope of the invention.Furthermore, any examples described herein are intended to aid inunderstanding the principles of the invention and are to be construed asbeing without limitation to such specifically recited examples andconditions. As a result, the invention is not limited to the specificembodiments or examples described below.

FIG. 1 is a block diagram of an exemplary wireless telecommunicationssystem operating in an RF band with a conflicting wireless system. Thewireless telecommunications system comprises an eNodeB 111communicatively coupled to a wireless telephony network 110. Generally,the eNodeB 111 is any system, apparatus, software, or combinationthereof operable to maintain or otherwise support wirelesscommunications, including data and voice, with subscribers via their UEs112 (e.g., mobile handsets and other wireless devices). In this regard,the eNodeB 111 may implement the wireless communications of the wirelesstelephony network 110 over RF via, for example, 2G, 3G, LTE, or thelike.

The conflicting wireless system comprises wireless access point (WAP)121 communicatively coupled to the wireless network 120. The wirelesssystem of the WAP 121 conflicts with the wireless telecommunicationssystem of the eNodeB 111 as the wireless system of the WAP 121 uses aform of wireless technology that is incompatible with the communicationprotocols of the wireless telecommunications system of the eNodeB 111.Thus, communications between the UE 112-2 and the WAP 121 can interferewith the communications between the UE 112-1 and the eNodeB 111.

To illustrate, the eNodeB 111 may be part of an LTE wireless telephonynetwork, whereas the WAP 121 may be part of a WiFi network (e.g., a WiFihotspot or a personal WiFi router). Generally, this means that theeNodeB 111 is operating in an unlicensed band of RF where WiFicommunications have flourished. Because these bands are so clutteredwith WiFi communications, WiFi devices (e.g., the UE 112-2) employListen Before Talk (LBT) to ensure that they do not interfere with oneanother when operating via WiFi. LTE communications, however, tend tooccupy an entire band of frequencies at any given time to ensure thattheir communications between their UEs 112 can be sustained. Thus, atthe very least, an LTE wireless telephony network will interfere withother communication systems in the band. So, to be more “friendly” withother wireless systems in an unlicensed band, the embodiments hereinprovide for LBT operations between the UE 112-1 and an eNodeB 111 of awireless telephony network 110.

The media access control (MAC) of LTE uses a centralized scheduler wherethe eNodeB 111 schedules UL and downlink (DL) traffic. LBT generallydoes not present problems on LTE DL transmissions because the eNodeB 112transmits when it has successfully contended for a channel ULtransmissions, however, are scheduled at precise instances of time andfrequency. And, LBT disrupts the timing of the scheduled ULtransmissions. But, the UE 112-1 needs to perform some form of LBTbefore each UL transmission because the channel may not be clear at thetime of its scheduled transmission.

One way to ensure fair coexistence between LTE-U and WiFi is to modifythe existing requirements to make it a “WiFi like” channel contentionalgorithm. In this regard, the UE 112-1 increases a size of a contentionwindow, in some embodiments doubling the size of the contention window.For example, a WiFi node (e.g., WAP 121) determines that a transmissionis successful if it receives an acknowledgement (ACK) shortly after thetransmission. The lack of an ACK means a collision has occurred. TheWiFi node, in turn, doubles the size (e.g., time) of its contentionwindow and re-contends for the channel LTE, however, has no suchmechanism.

Generally, if data received by the eNodeB 111 has an error, the eNodeB111 buffers the data and sends a NACK, which prompts a re-transmissionfrom the UE 112-1. When the eNodeB 111 receives the re-transmitted data,the eNodeB 111 combines that data with buffered data for errorcorrection. This process may still occur but it is enhanced with theincrease of the contention window size. One existing mechanism is HybridARQ (HARQ). The embodiments herein provide a new mechanism to the PHYlayer for LTE in this feedback process in addition to the existing HARQmechanism at the MAC and PHY layers to ensure fast re-transmission andhigher data rates.

In order to reduce the delay of the feedback loop needed to increase thecontention window at the UE 112-1, the eNodeB 111 sends anon-acknowledgement (NACK) via a Short Control Signal (SCS), denoted asSCS NACK, without performing LBT, immediately after or shortly after thereception of the data. The SCS can be sent without performing LBT aslong as the SCS duty cycle is under 5% of the maximum transmission timeof the node, according to European Union standards.

Neighboring nodes perform LBT prior to transmission and “backoff” uponsensing the channel is busy after the transmission of the HARQ NACK.However, in LTE, the eNodeB 111 needs more processing time to performerror correction and soft combining on received data before determiningwhether a HARQ ACK or a HARQ NACK should be sent. Therefore, in additionto transmitting error correction codes (ECC) with data, the UE 112-1includes a cyclic redundancy check CRC, which is generally short and haslittle impact on the efficiency of a payload such that an error can bedetected more quickly. And, when an error is detected, an SCS NACK to besent without LBT within a short time window after the data has beenreceived by the eNodeB 111 to provide a relatively low probability ofcollision.

FIG. 2 is a flowchart illustrating an exemplary process 200 operablewith the eNodeB 111 in the wireless telecommunications system. In thisembodiment, the eNodeB 111 receives the transport block of data from theUE 112-1, in the process element 201. The eNodeB 111 then uses a CRC inthe transport block of data to determine a checksum of the data, in theprocess element 202. If the data passes the checksum (process element203) then the eNodeB 111 processes the data and waits to receive anothertransport block of data from the UE 112-1, in the process element 201.

However, if the checksum fails, the eNodeB 111 transmits a NACK to theUE 112-1 such that the UE 112-1 can increase its contention window, inthe process element 204. For example, the eNodeB 111 may use SCS toimmediately transfer a HARQ NACK to the UE 1112-1 to ensure that theconflicting wireless communications between the UE 112-2 and the WAP 121do not have time to contend for the channel. At about the same time, theeNodeB 111 stores the data of the transport block in a buffer, in theprocess element 205, to begin correcting errors on the data of thetransport block using the ECC provided by the transport block, in theprocess element 206.

If the errors are corrected in the data using the ECC (process element207), the eNodeB 111 transmits an ACK to the UE 112-2 and waits for thenext transport block, in the process element 201. If this ACK isreceived by the UE 112-1 during the increased contention window of theUE 112-1, then the UE 112-1 may decrease the contention window back toits original size (e.g., amount of time) to resume normal operations. Ifthe errors, however, are not corrected by the ECC, then the eNodeB 111may begin correcting the errors with soft error correction, in theprocess element 208, upon reception of the same transport block from theUE 112-1. For example, the eNodeB 111 may combine the data of bothtransport blocks to determine errors in the data. Alternatively oradditionally, the eNodeB 111 may use the CRC and/or the ECC of thesubsequent transport block to determine the errors.

FIG. 3 is a flowchart illustrating an exemplary process 250 operablewith the UE 112-1 in the wireless telecommunications system. In thisembodiment, the UE 112-1 transmits a transport block of data to theeNodeB 111, in the process element 251. The transport block of data, asmentioned above, includes a CRC for the eNodeB 111 to perform a quickerror check on the data of the transport block. And, if the data of thetransport block contains errors, the eNodeB 111 immediately sends a NACKto the UE 112-1 (e.g., a HARQ NACK via SCS). In this regard, the UE112-1 receives the NACK, in the process element 252, and increases itscontention window, in the process element 253.

If an ACK is received by the UE 112-1 from the eNodeB 111 during theincreased contention window, the UE 112-1 transmits its next transportblock of data to the eNodeB 111, in the process element 251. Otherwise,the UE 112-1 may re-transmit the transport block of data to the eNodeB111, in the process element 255.

In some embodiments, when the data of the transport block has expired,the UE 112-1 discards the data and the transport block. For example, thetransport block may include a relatively small portion of voice dataduring a call of the UE 112-1. Dropping that relatively small portion ofvoice data may have a negligible effect on the overall voiceconversation. Accordingly, the UE 112-1 may conclude that the transportblock is no longer valid and drop the transport block fromretransmission altogether.

FIGS. 4-6 are exemplary messaging diagrams between the UE 112-1 and theeNodeB 111 in the wireless telecommunications system. The messagingdiagram of FIG. 4 shows a successful transmission of data with thetransport block to the eNodeB 111. Upon receiving the transport blockfrom the UE 112-1, the eNodeB 111 performs the CRC check. As theresulting checksum has passed the CRC check, the eNodeB 111 sends theSCS ACK to the UE 112-1 as is typical in LTE communications.

The messaging diagram of FIG. 5 illustrates when the data of thetransport block fails the CRC check. In this regard, the eNodeB 111transfers an SCS NACK to the UE 112-1, which in turn, increases itscontention window. During this time, the eNodeB 111 performs errorcorrection using the ECC in the transport block. If the ECC successfullycorrects the data of the transport block, the eNodeB 111 transfers aHARQ ACK to the UE 112-1 so that it may reset his contention window backto its original size.

The messaging diagram of FIG. 6 illustrates when both the CRC check andthe ECC both fail. Since a SCS NACK has already been sent by the eNodeB111 upon a failed CRC check, the eNodeB 111 does not need to send a HARQNACK when the ECC fails also. An SCS NACK is an indication from theeNodeB 111 to the UE 112-1 to retransmit its transport block. Again, theUE 112-1 increases its contention window and retransmits a transportblock to the eNodeB 111. The eNodeB 111 combines the data of theretransmitted transport block to perform a soft error correction usingthe ECC. If the soft error correction has passed, then the eNodeB 111transmits an HARQ ACK to the UE 112-1 such that the UE 112-1 can resetits contention window.

FIG. 7 is a flowchart illustrating another exemplary process operable275 with an eNodeB 111 in the wireless telecommunications system. Inthis embodiment, the eNodeB 111 receives a transport block of data froma UE 112, in the process element 276. Within the transport block is aCRC that is used to check the integrity of the data. In this regard,eNodeB 111 determines a checksum of the data based on the CRC of thetransport block, in the process element 277. If the checksum passes(process element 278), then the eNodeB transmits an SCS ACK to the UE112, in the process element 279 and the process ends, in the processelement 280 (i.e., until the UE 112 needs to send another transportblock of data).

If the checksum fails (the process element 278), then the eNodeB 111transmits an SCS NACK of the transport block to the UE 112, in theprocess element 281. The eNodeB 111 stores the transport block of datain a buffer, in the process element 282, and then correct the errors onthe transport block using the ECC in the transport, in the processelement 283. If the errors are corrected (process element 285) then theeNodeB 111 transmits a HARQ ACK to the UE 112, in the process element284, and the process ends, in the process element 280, until the UE 112needs to transmit another transport block to the eNodeB 111.

If the errors in the transport block cannot be corrected (i.e., theprocess element 285), then the eNodeB 111 determines whether a re-tryattempt has exceeded its timer, in the process element 286. If the timerhas not expired, then the eNodeB 111 may end the process 275, in theprocess element 280, until the UE 112 needs to send another transportblock. If the timer has expired, then the eNodeB 111 may send a HARQNACK to the UE 112, in the process element 287, to end the process 275until the UE 112 needs to transmit another transport block the eNodeB111.

FIG. 8 is a flowchart illustrating another exemplary process 290operable with a UE 112 in the wireless telecommunications system. Inthis embodiment, the UE 112 transmits a transport block of data to aneNodeB 111, in the process element 291. Then, the UE 112 determineswhether it has received an SCS NACK, an SCS ACK, a HARQ ACK, or a HARQNACK, in the process element 292.

If the UE 112 receives an SCS NACK, then the UE 112 increases acontention window, in the process element 297, and retransmits thetransport block, in the process element 298. Then, the process 290 ends,in the process element 299, until the UE 112 needs to transmit anothertransport block.

If the UE 112 receives an SCS ACK or a HARQ ACK, then the UE 112debuffers the transport block, in the process element 293. For example,as the transport block is successfully received by the eNodeB 111, theUE 112 no longer has a need to retain the transport block. Accordingly,the UE 112 removes the transport block from transmission such thatanother transport block can be transmitted. From there, the UE 112resets its contention window, in the process element 294, and theprocess 290 ends, in the process element 299 (i.e., until the UE 112needs to send another transport block of data).

If the UE 112 receives a HARQ NACK, the UE 112 increases its contentionwindow, in the process element 295, and retransmits the transport block,in the process element 296. This allows the eNodeB 111 to correct theerrors in the transport block via soft combining and/or error correction(e.g., via the ECC of the transport). Then, the process 290 ends, in theprocess element 299 (i.e., until the UE 112 needs to send anothertransport block of data).

The invention can take the form of an entirely hardware embodiment, anentirely software embodiment or an embodiment containing both hardwareand software elements. In one embodiment, the invention is implementedin software, which includes but is not limited to firmware, residentsoftware, microcode, etc. FIG. 7 illustrates a computing system 300 inwhich a computer readable medium 306 may provide instructions forperforming any of the methods disclosed herein.

Furthermore, the invention can take the form of a computer programproduct accessible from the computer readable medium 306 providingprogram code for use by or in connection with a computer or anyinstruction execution system. For the purposes of this description, thecomputer readable medium 306 can be any apparatus that can tangiblystore the program for use by or in connection with the instructionexecution system, apparatus, or device, including the computer system300.

The medium 306 can be any tangible electronic, magnetic, optical,electromagnetic, infrared, or semiconductor system (or apparatus ordevice). Examples of a computer readable medium 306 include asemiconductor or solid state memory, magnetic tape, a removable computerdiskette, a random access memory (RAM), a read-only memory (ROM), arigid magnetic disk and an optical disk. Some examples of optical disksinclude compact disk-read only memory (CD-ROM), compact disk-read/write(CD-R/W) and DVD.

The computing system 300, suitable for storing and/or executing programcode, can include one or more processors 302 coupled directly orindirectly to memory 308 through a system bus 310. The memory 308 caninclude local memory employed during actual execution of the programcode, bulk storage, and cache memories which provide temporary storageof at least some program code in order to reduce the number of timescode is retrieved from bulk storage during execution. Input/output orI/O devices 304 (including but not limited to keyboards, displays,pointing devices, etc.) can be coupled to the system either directly orthrough intervening I/O controllers. Network adapters may also becoupled to the system to enable the computing system 300 to becomecoupled to other data processing systems, such as through host systemsinterfaces 312, or remote printers or storage devices throughintervening private or public networks. Modems, cable modem and Ethernetcards are just a few of the currently available types of networkadapters.

What is claimed is:
 1. A method operable with a Long Term Evolution (LTE) communications operating in a radio frequency (RF) band comprising a conflicting wireless technology, the method comprising: processing a transport block of data from a user equipment (UE) at an eNodeB, the transport block comprising a cyclic redundancy check (CRC); determining a checksum of the transport block based on the CRC at the eNodeB; failing the checksum; transmitting, from the eNodeB to the UE, a non-acknowledgement (NACK) of the transport block based on the failed checksum; in response to the UE receiving the NACK, increasing a contention window at the UE; and re-transmitting the transport block from the UE to the eNodeB.
 2. The method of claim 1, wherein: the transport block further comprises an error correction code (ECC); and the method further comprises, at the eNodeB: storing the transport block in a buffer; correcting errors on the transport block using the ECC; and sending an acknowledgement (ACK) of successful receipt of the transport block to the UE in response to correcting the errors.
 3. The method of claim 2, further comprising, at the UE: receiving the ACK within the increased contention window; and resetting the contention window to its original size in response to receiving the ACK.
 4. The method of claim 1, wherein: transmitting the NACK further comprises configuring the NACK in a Short Control Signal (SCS) to the UE.
 5. The method of claim 1, further comprising: receiving another transport block of data from the UE at the eNodeB, the other transport block comprising another cyclic redundancy check (CRC); determining a checksum of the other transport block based on the CRC at the eNodeB; passing the checksum; and transmitting, from the eNodeB to the UE, an acknowledgement (ACK) of successful receipt of the other transport block.
 6. The method of claim 1, wherein: the ACK is a Hybrid Automatic Repeat Request (HARQ) ACK.
 7. The method of claim 1, wherein: the RF band is a WiFi band.
 8. A system operable with a Long Term Evolution (LTE) communications operating in a radio frequency (RF) band comprising a conflicting wireless technology, the system comprising, comprising an eNodeB; and a user equipment (UE); wherein the eNodeB is operable to process a transport block of data from the UE, the transport block comprising a cyclic redundancy check (CRC), the eNodeB being further operable to determine a checksum of the transport block based on the CRC, to fail the checksum, and to transmit a non-acknowledgement (NACK) of the transport block to the UE based on the failed checksum; wherein the UE is operable to receive the NACK, to increase a contention window, and to re-transmit the transport block to the eNodeB.
 9. The communication system of claim 8, wherein: the transport block further comprises an error correction code (ECC); and the eNodeB is further operable to store the transport block in a buffer, to correct errors on the transport block using the ECC, and to send an acknowledgement (ACK) of successful receipt of the transport block to the UE in response to correcting the errors.
 10. The communication system of claim 9, wherein: the UE is further operable to receive the ACK within the increased contention window, and to reset the contention window to its original size in response to receiving the ACK.
 11. The communication system of claim 8, wherein: the eNodeB is further operable to transmit the NACK by configuring the NACK in a Short Control Signal (SCS) to the UE.
 12. The communication system of claim 8, wherein: the eNodeB is further operable to receive another transport block of data from the UE, the other transport block comprising another cyclic redundancy check (CRC), the eNodeB being further operable to determine a checksum of the other transport block based on the CRC, to pass the checksum, and to transmit an acknowledgement (ACK) of successful receipt of the other transport block to the UE.
 13. The communication system of claim 8, wherein: the ACK is a Hybrid Automatic Repeat Request (HARQ) ACK.
 14. The communication system of claim 8, wherein: the RF band is a WiFi band.
 15. A non-transitory computer readable medium comprising instructions that, when executed by a processor of an eNodeB employing Long Term Evolution (LTE) communications operating in a radio frequency (RF) band comprising a conflicting wireless technology, the instructions directing the processor to: process a transport block of data from a user equipment (UE), the transport block comprising a cyclic redundancy check (CRC); determine a checksum of the transport block based on the CRC; fail the checksum; and transmit a non-acknowledgement (NACK) of the transport block to the UE based on the failed checksum that directs the UE to increase a contention window at the UE and re-transmit the transport block to the eNodeB.
 16. The computer readable medium of claim 15, wherein: the transport block further comprises an error correction code (ECC); and the instructions further direct the processor to store the transport block in a buffer, correct errors on the transport block using the ECC, and to send an acknowledgement (ACK) of successful receipt of the transport block in response to correcting the errors.
 17. The computer readable medium of claim 16, wherein: the UE is further operable to receive the ACK within the increased contention window, and to reset the contention window to its original size in response to receiving the ACK.
 18. The computer readable medium of claim 15, wherein the instructions further direct the processor to: configure the NACK in a Short Control Signal (SCS) to the UE.
 19. The computer readable medium of claim 15, wherein the instructions further direct the processor to: receive another transport block of data from the UE at the eNodeB, the other transport block comprising another cyclic redundancy check (CRC); determine a checksum of the other transport block based on the CRC at the eNodeB; pass the checksum; and transmit an acknowledgement (ACK) of successful receipt of the other transport block to the UE.
 20. The computer readable medium of claim 15, wherein: the ACK is a Hybrid Automatic Repeat Request (HARQ) ACK. 